Electromechanical translating device



Nov. 5, 1935.

o. M. DU NNING ELECTROMECHANICAL TRANSLATING DEVICE Filed June 4, 1932 2Sheets-Sheet 1 ZSnventor ORVILLE M.DUNN|N&

attorney,

Nov. 5, 1935'. o. M. DUNNING 2,020,139

ELECTROMECHANI GAL TRANSLATING DEVICE Filed June 4, 1952 2 Sheets-Sheet2 7 68 8 67 6s 3 I 61 g 81 1-60 Zhwentor URVILLE M.Du-lw/vc+ 85 Ha a(Ittomeg Patented Nov. 5, 1935 UNITED STATES tonne PATENT OFFICEELECTROMECHANICAL TRANSLATING DEVICE Application June 4, 1932, SerialNo. 615,306

15 Claims.

Electro-mechanical translating devices are used to change mechanicalvibration into corresponding electrical impulses. The embodiments of myinvention specifically described are directed to translating devicesespecially adapted for use as phonographic reproducers, but the generalprinciples may also be applied to many other types of electro-mechanicaltranslating devices such as, for instance, a. microphone.

The performance of a phonographic reproducer may, in general, be judgedupon three fundamental characteristics. These characteristics are first,the range and uniformity of response to the various frequencies whichare impressed upon the reproducer; second, the sensitivity of thedevice; and third, the mechanical impedance at the stylus point.

The range and uniformity of response of a reproducer to variousfrequencies gives ameasure of the exactness with which the reproducerwill translate mechanical vibrations into electrical vibrations. It isnearly always desirable that the range be as great as possible and thatthe response be uniform to frequencies over substantially the entirerange in order that the voltage generated in the rep-reducer may closelycorrespond to the vibrations engraved upon the record.

The second characteristic mentioned, namely, the sensitivity of thedevice, may or may not be of great importance in anyparticularapplication.

It is, of course, always possible to employ a thermionic amplifier tomagnify the current generated by the reproducing device, but in anyspecific case, the degree of amplification required is determined by thesensitivity of the reproducer. With a reproducer of high sensitivity, itis possible to employ very simple amplifying apparatus or to eliminateamplifying apparatus entirely with a consequent reduction in the cost,complexity, distortion, and likelihood of failure in the, system. Highsensitivity is therefore, in most cases, an extremely desirable feature.

The third characteristic, namely, the mechanical impedance of thereproducer as viewed from the stylus point, isthe factor whichdetermines the extent of destructionof the record groove and of thestylus in the operation of a reproducer. It is always desirable that thewear on the record and the reproducer stylus be very small to insurelong life. It is extremely important in the case of wax records that themechanical impedance of the reproducer be kept very low to preventserious damage to the record groove during th process of reproducing.

The range and. uniform y of resp e o a r o-rnographic reproducer aredetermined by the arrangement and the values of the masses andcompliances of the various moving parts of the reproducer and by thecompliance of the record grooves. The compliance of the record groovesis usually a predetermined factor and limits the design of the movingparts of the reproducer.- In most cases, if the reproducer is totranslate the higher frequencies without distortion, it is necessarythat the mass of the moving parts of the reproducer be held to thelowest possible value. In most types of reproducers, this desirable lowmass cannot be attained without an accompanying low sensitivity and inmany cases it may be impossible to attain a sufficiently low mass toreproduce frequencies of the order of 4000 to 5000 cycles withoutreducing the sensitivity to a point where an impracticably high degreeof amplification is necessary to raise the sound to the desired level.

The sensitivity of an electrical reproducer is determined by a number offactors, of which probably the most important is the translating mediumwhich actually generates the voltages corresponding to the mechanicalvibrations impressed upon the device. The medium most commonly used inelectrical reproducers is that of an iron vane vibrated in a magneticfield and surrounded by a coil wherein such voltages are generated. Thistype of translating medium has, in practice, a fundamentally lowsensitivity which it is not practical to increase when the range offrequency response and the mechanical impedance are considered. On theother hand, the granular carbon cell is normally a relatively highsensitivity device since it draws energy from an external source and, inconsequence, acts as an amplifier of the electrical energy derived fromthe mechanical vibrations. The granular carbon cell will produce avoltage many times that of the magnetic translating medium for anequivalent displacement under ordinary phonographic conditions. However,the granular carbon cell is not suited for direct connection to thevibrating stylus of a reproducer as is the magnetic medium.

Phonographic records are cut with the so-called constant velocitycharacteristic-that is, assuming a sinusoidal wave form, the product ofthe maximum amplitude of each cycle of the groove multiplied by itsfrequency is a constant for uniform loudness through the range offrequencies recorded. In such a record, the maximum velocity in eachcycle imparted to a stylus driven thereby will be a constant for allfrequencies While the maximum amplitude in each cycle s inverselyproportional to the frequency for constant loudness. The granular carboncell, however, is independent of the velocity of motion, the

voltage generated being determined by the amplitude only of vibration.It is therefore apparent that if a granular carbon cell were vibratedwith the amplitude proportional to that engraved upon the phonographrecord, the resulting response would not be uniform for all frequencies,but would rather exaggerate the lower frequencies in comparison to thehigher frequencies. If a granular carbon cell is to be used as atranslating medium, it is therefore essential that some form ofcompensation be introduced in order to secure uniform response to allfrequencies from a recording of the constant velocity type. While thegranular carbon cell has been employed in phonographic reproducers inthe past, such reproducers necessarily produced a certain amount ofdistortion since the compensation usedtherein was not operative over awide range of frequencies.

' The mechanical impedance of a reproducer as viewed from the stylusshould always be as low as possible in order to minimize the wear of anddamage to both the stylus and the record groove. This requiresparticularly that the stiffness of the reproducer as viewed from thestylus be made as small as possible, and, coupled with the requirementof a large frequency range, necessitates-theuse of extremely smalleffective masses.

It is an object of this invention to provide an electro-mechanicaltranslating device which will havev substantially uniform response to awide range of frequencies.

Another object of this invention is to attain high sensitivity in atranslating unit without the introduction of serious distortion. It is afurther object of this invention to provide a phonographic reproducerhaving extremely low mechanical impedance as viewed from the stylus.

It is a further object of this invention to provide a phonographicreproducer having the combination of a wide frequency range,substantially uniform response through the frequency range, highsensitivity, and low mechanical impedance at its stylus.

It is still a further object of this invention to provide a translatingdevice wherein the translating medium produces a voltage proportional toamplitude of vibration only, and wherein a transmitting and compensatingmeans is provided to actuate said translating medium and to produce anamplitude of vibration at said translating meillustrate the principlesinvolved therein. One of these embodiments is a reproducer forvertically cut records, and the other, a reproducer for laterally cutrecords.

The devices shown herein as illustrative of my invention, may begenerally described as a system comprising, first, a pair of relativelymovable spaced plates separated by a viscous fluid and so designed as tospacing and area that the principal reaction to relative movement Of theplates is one of viscosity, wherein the force opposing the impressedmotion is directly proportional to the velocity of the motion; second, astylus or other means arranged to transfer the vibrations engraved in aphonographic record or other me- 5 chanical vibrations to one of theabove mentioned spaced plates; and. third, a translating medium having amovable element which is connected to the other one of the abovementioned pair of spaced plates and which is so designed that its nchief mechanical impedance over the range of frequencies to bereproduced, is one of compliance. If, then, a vibration is impressed bythe stylus or other vibration transferring means upon the associatedplate, a force proporticnal to the veloc- 15 ity of the vibration willbe transmitted to the other plate. The latter plate is connected to thesaid movable element of the translating medium, the principal reactionof which part, over the range of frequencies of interest, is one ofcompli- 20 ance. Since a force applied to a compliance will a result ina displacement directly proportional to the force, it is obvious thatwhen a constant sinusoidal velocity is applied to the stylus a constantsinusoidal amplitude of motion in the said movable element of thetranslating medium will result. If the translating medium, therefore, isone of a type which produces a voltage proportional to its amplitudeonly, it will produce a voltage proportional to the velocity of thestylus 30 or other vibration transferring means.

For a cleareriunderstanding of my invention, reference may be had to thedrawings accompanying and forming part of this specification, wherein:35

Figure 1 is an elevational view, with parts broken away, of one form ofmy invention as embodied ina reproducer for vertical cut records;

' shown in Fig. l with the cover removed;

Fig. 6 is the equivalent electrical circuit of the mechanical vibratorysystem of the translating 50 unit shown in Fig. 1;

Fig. 7 is a plan View of another form of my invention as embodied in areproducer for lateral cut records;

Fig. 8 is a plan view, partly broken away, of the translating unit shownin Fig. 7;

Fig. 9 is a longitudinal vertical sectional view of the translating unitshown in Fig. '7; and

Fig. 10 is a fragmental side view of the repro ducer shown in Fig. 7.

. In Fig. 1, one form of my improved translating unit is shown asembodied in a reproducer "applied to a dictating machine having an arm Iadapted to be fed transversely across a cylindrical record 2 by means ofa feed screw or other suitable mechanism (not shown). The arm isprovided with an opening 3 in which the reproducer is suspended. At itsouter end, the arm I has a bifurcated projecting lug 4. A bracket 5 ispivotally mounted within the fork of the lug 4 by means of a pin 6.Bracket 5 has a U-shaped projection of which the upper arm is suitablydrilled to receive the upper conical end of a short shaft 1 fixedlymounted in a block 1 which is secured to a mounting bracket 8. A lowerpivot bearing for the shaft 1 is formed in a set screw (not shown)threaded in the lower arm of the U-shaped bracket 5 and held in place bya lock nut 9, so that the pressure on the pivots may be adjusted.

A base plate 8 is secured to the mounting bracket 8 and serves as asupport for the parts of the reproducer. A granular carbon cell of wellknown construction is mounted on the base plate 8 by means of a bracketl l which is held in place by a screw ll threaded into the base plate.The granular carbonfcell comprises acup l0 secured to the bracket H by ascrew l2 and a nut I4 which are insulated from the bracket and the cupby means of an insulating bushing l6 and an insulating washer IS. Thescrew I2 is provided at its inner end with a head l3 forming anelectrode which may be carbon faced. A terminal I8 is provided forconnection to the rear electrode I3. The inside of the cup In is insulated by paper or other insulating material l9. A diaphragm 2B is heldagainst and electrically connected to the cup H] by means of a threadedshouldered annulus 22. A washer 2| of paper is provided between theshoulder of annulus 22 and the diaphragm 20 to clamp the diaphragmfirmly. Electrical connection is made to the diaphragm 20 through thecup l0 and a terminal 23 which is insulated from the bracket l I. by awasher 24 of fiber or other insulating material. The interior of the cupHi is filled slightly more than half-way by carbon granules 25 similarto those in common use for microphones.

To the front of the diaphragm 2B is fastened a small cup 26 which may besecured by soldering or other suitable manner. To the cup 26 is fasteneda bent arm 21 of decreasing and circular cross section. The arm 21 andthe cup 26 are preferably formed of light thin metal and may beconstructed by electroplating on a suitable form with nickel to athickness of .002 to .003 inch.' The lower end of the arm 21 is closedand forms a small flat horizontal plate.

The right hand end,of the base plate 8 is provided with a circularopening 28 having a shoulder 29. A diaphragm 31 is mounted within theshouldered opening 28. A washer 30 is disposed on each side of diaphragm3|. This diaphragm is secured in place by a threaded annulus 36 which isscrewed into a threaded collar 31. The collar 31 is held in place on thebase plate 8 by means of suitable screws 38. A washer or gasket 39 isprovided between the collar 31 and the base plate 8. The diaphragm 3|carries a stylus holding member 33 preferably made of a strong alloy ofaluminum or magnesium. Stylus holder 33 has a flange 34 bearing againstthe lower side of the diaphragm and an upwardly extending portion (notshown) which is secured to a washer 35 on the upper side of thediaphragm. A gap 40, which in this case is or" 'the order of .010" inthickness'is formed between the upper side of the diaphragm and thelower flat end of the arm 21. A stylus 32 is provided for engagementwith the record groove of the cylinder 2. The cup formed by the annulus36 and the diaphragm Si is filled with a suitable liquid 4| of desiredviscosity. This liquid may, for example, be composed of a thickvegetable oil and a solvent.

The whole translating unit may be protected by means of a cover 42 whichis arranged to make the entire unit oil-tight. A limit pin 43 fastenedin the arm I cooperates with a V-shaped limit loop 44 on the case 42 ina well known manv ner so that as the arm I is raised, the reproducer iscentered and raised from the surface of the record. The terminals 23 and18 of the granular carbon cell are respectively connected to terminals45 and 46 in cover 42. The circuit in which the unit is connected, asshown in Fig. 3, is from the terminal 23 to terminal 45, to a battery41, to the primary of a suitable transformer 48, to terminal 46, and toterminal IS. The secondary of the transformer may be connected to a headphone 49 or to any other desired device for relaying the impulses.

The operation of the device above described is as follows: The stylus 32is pressed against the record groove on the cylinder 2 by the weight ofthe translating unit. As the cylinder is revolved the stylus is vibratedin accordance with the depth of the groove and consequently causes thediaphragm 3l to vibrate in the same manner. The vibration of thediaphragm results in a reaction proportional to the velocity of thevibration, due to the viscosity of the fluid disposed within thecup-shaped member 36 and acting in the gap 40 formed by the diaphragm 3|and the adjacent end of the arm 21. The force acting on the'end of thearm 21 will, therefore, be proportional to the velocity of the stylus.This vibratory force acting upon the flattened end of the arm 21 tendsto move the arm 21 about a horizontal line through the center of thediaphragm 20. As will be seen from Fig. 5, if the force on the end ofthe arm 21 is in an upward direction the diaphragm 20 will be deflectedoutwardly below the said central horizontal line and inwardly above suchline. If the force on the end of the arm 21 is downward, the oppositeaction will take place and the lower portion of the diaphragm 26. willbe deflected inwardly and'the upper portion deflected outwardly. Withthis arrangement, the carbon granules within the cup I [I will becompressed and relieved in accordance with the motion of the arm 21. Itis to be understood that the construction consisting of arm 21 anddiaphragm 20 acts as a bell crank or similar structure pivoted on ahorizontal line through the center of the diaphragm 20 and that themotion imparted to the diaphragm 26 will have a smaller amplitude thanthe motion of the lower end of arm 21 by reason of the differences inthe lever' arms from the center of rotation to the points of applicationof the force.

Change in pressure on the carbon granules 25 changes the electricalresistance of the path through these granules, and consequently changesthe current flowing through the circuit and supplied by the battery 41.The vibratory current generated will be proportional to the displace- Itis extremely important therefore that the mass 7 of the arm 21 be keptas low and the stiffness thereof as great as possible. The diaphragm 26should be made of such stifiness that its efiective value when viewedfrom the end of the arm 2? is sufficient to cause resonance with theeffective mass of the arm 21'to occur at a frequency near the upperlimiting frequency of the system.

of such a transformer.

Furthermore, it is extremely desirable to hold the mass and thestiffness of the diaphragm 3| to the lowest possible values. In theparticular embodiment shown the diaphragm preferably has a free diameterof approximately inch and is preferably formed of aluminum alloy .002"thick. The stylus holding member is formed of one of the strong alloysof aluminum or magnesium and is given the minimum possible dimensionsconsistent with safety in view of accidental stresses to which it may besubjected. The effective mass of the stylus, stylus holder and diaphragmas described in this embodiment is preferably approximately .012 gram.

In order to operate most effectively, certain limitations must be placedupon the design of the various parts. For best results, it is importantthat the reaction resulting from the two spaced plates, formed by thediaphragm 3| and the end of the arm 21, with the intervening viscousmedium, be proportional to the velocity of the impressed motion only. Ifthe gap is made too small and/or the opposed areas of the plates is toolarge, the reaction will to some extent be one of compliance, while ifthe gap is made too large there will be an appreciable mass reaction.However, by properly dimensioning this gap, the reaction can be madesubstantially proportional to the velocity of motion only. It isfurthermore desirable that the impedance of the structure comprising thearm 21 and the diaphragm 20 be higher than the impedance of the pair ofspaced plates with theintervening viscous fluid at all frequencies whichare to be reproduced. If this is not true, the reaction of the spacedplates and the interposed fluid will not control the motion of thediaphragm 20 as described above, and the response of the device todifferent frequencies will not be uniform.

The operation of the device above described may also be explained byusing the electrical analogs of the various parts comprising thestructure. Fig. 6 shows an electrical circuit which is equivalent to themechanical structure of the translating unit of Fig. 1. In this figurethe capacity cl represents the compliance of the record groove; theinductance ml represents the effective mass of the stylus, stylus holderand diaphragm; the capacity 02 represents the compliance of thediaphragm 3|; the resistance R represents the impedance of the twospaced plates formed by the diaphragm 3| and the lower end of arm 21with the intervening viscous fluid; the inductance m2 represents theeffective mass of the arm 21 and the diaphragm 26 as viewed from thelower end of arm 21; and the capacity 03 represents the compliance ofthe diaphragm 20 as viewed from the lower end of the arm 21. It will beunderstood that the mechanical structure of the arm 21 with thediaphragm 20 is equivalent to an electrical transformer which is notshown, but which does not affect the frequency characteristic of theunit. In the above description, therefore, by the effective values ofthe inductance m2 and the compliance 03 are meant the values as seen onthe primary side Now it may be considered that the record is sending analternating current of constant amplitude through the network at allfrequencies of interest. If the impedance of the circuit through theinductance ml, the capacity 02, and the resistance R, is made lower atall frequencies of interest than the impedance of the path through theinductance ml, the capacity 02, the inductance m2,

andcapacity 03 or the circuit through the capacity cl, most of thecurrent flowing into the network will flow through the resistance R.Since this current is assumed of constant amplitude, the voltage acrossthe resistance R will be of constant amplitude throughout the range offrequencies. The voltage of constant amplitude across the resistance Ris therefore applied across the inductance m2 and the capacity 03. Sincethe capacity 03 is made to have a higher impedance at all frequencies ofinterest than the 4 inductance m2, it is the limiting impedance in thisbranch circuit and in consequence the amplitude of the current flowingthrough this circuit will be principally determined by it. The impedanceof a capacity decreases with frequency and in consequence the amplitudeof the current through this branch circuit will increase in proportionto the frequency of the applied voltage. If we have a current flowingthrough a condenser which has an amplitude proportional to the frequencywe may define the current mathematically as i=A-w sin wt where A is aconstant and w is 211' times the frequency. If then we integrate i withrespect to t, we will obtain Q, the charge. Then Now the charge in anelectrical circuit is analogous to displacement in a mechanical systemand from the above equation it is obvious that the amplitude of thedisplacement of the diaphragm 20 is independent of the applied frequencyand constant under the conditions described above where a vibrationhaving a velocity of constant amplitude is applied to the stylus.

Figs. '7 to 10 show a modification of my invention indicating in ageneral form the application thereof to a reproducer for laterally cutdisc records. A disc record Bl is carried on a rotatable turntable 60.An arm 62 mounted on a vertical pivot (not shown) is provided forsupporting the reproducer. The reproducer comprises a casing 63 which issuitably fixed to the arm 62. At its left hand end the casing 63 isthreaded to receive a flanged ring 64. On its lower side the ring 64 isprovided with two lugs 65 and 66. A small light shaft 68 is pivotedbetween the lugs 65 and 66. The lug 65 is provided with a cone bearingsurface and the lug 66 is provided with a screw ll drilled to accept theconical end of the short shaft 68, thus allowing adjustment of thepressure on the pivots. lock the screw H in desired position. The shortshaft 68 is drilled vertically to receive a stylus 61. It is alsodrilled and threaded axially to reserve a stylus holding screw 10 whichlocks the stylus 61 rigidly in place. At its upper end the stylus 61coacts with a V-shaped notch 13 in a light hollow cylindrical member 69.Member 69 may be riveted or otherwise suitably fastened to a diaphragm14. The diaphragm I4 is held in place by the flanged ring 64 and ashouldered cylindrical member 15. A washer 16 is provided between thediaphragm l4 and the member 15 to securely hold the diaphragm and torender the construction oil-tight. At its right hand enlarged end, thecylindrical member 15 is threaded to receive a cup 11 of a granularcarbon cell. A diaphragm 18 is clamped tightly in place between the cup11 and the shoulder of member 15, as shown in Fig. 9. A soft washer 19is provided between the diaphragm l8 and the member A nut 12 is providedto 15 to clamp the diaphragm evenly around its periphery and to providean oil-tight joint. A tapering cup-shaped member is fastened to thefront of the diaphragm 18 by means of a small attachment member 8! whichmay be soldered or otherwise fastened to the diaphragm 18 and saidmember 80. The flat end of the member 80 is placed opposite the centerof the diaphragm i4 and is spaced'about .010 inch away. The spacebetween the diaphragms 14 and i8 is partially filled with a viscousmaterial as described hereinbefore. The two spaced plates, formed by theend of member 80 and the opposed portion of diaphragm 14, together withthe intervening viscous material, serve as a means of transmission ofthe vibrations from the stylus to the granular carbon cell. Theconstruction of the granular carbon cell is similar to that previouslydescribed hereinbefore and comprises a threaded stud having a head 84constituting a rear electrode, internal insulation 92 within the cup 11,carbon granules 83, terminals 86 and 81, a flanged insulating bushing88, and a nut 89. Connections to the granular carbon cell are broughtout through a two conductor cable fastened in an insulating bushing 9|in casing 63.

The operation of this reproducer for lateral cut records is equivalentto that of the reproducer for vertical cut records previously described.The only substantial difference in the operation is that the diaphragmof the carbon cell has the same amplitude of vibration as the drivenplate formed by the ends of the member 89, whereas, in the previouscase, a step-down leverage was used so that the amplitude of vibrationof the diaphragm was less than the amplitude of the plate formed on thelower end of the arm 21. In this case also the applied forces tend tomove the diaphragm as a whole, that is, these forces on the diaphragmtend to translate it rather than to rotate it. The equivalent electricalcircuit of Fig. 6 may also be applied to this form of reproducer whereinthe capacity cl represents the compliance of the record groove; theinductance ml represents the combined effective mass of the stylus Bl,the shaft 58, the projecting member 69, and the diaphragm M; thecapacity 02 represents the compliance of the diaphragm M; the resistanceR represents the impedance of the two spaced plates formed by thediaphragm l4 and the opposed end of the member 89 with the interveningviscous fluid; the inductance m2 represents the effective mass of themember 80 and the diaphragm l8, and the capacity 03 represents thecompliance of the diaphragm 18. It is to be understood that the variouslimitations applied to the design of the reproducer for vertical cutrecords previously described should preferably be applied to the designof this reproducer.

The structures hereinbefore described for transmitting vibrations fromsound records to the translating medium may also be applied to manyother forms of translating mediums than the granular carbon cell. It iswell known that there are other forms of translating mediums wherein thevoltage produced is independent of the velocity of motion and dependsonly uponthe amplitude of the vibrations. Any of these devices thereforeare applicable for use in this type of reproducer and may be substitutedfor the granular carbon cell of the embodiments described herein. Asexamples of other devices which might be substituted for the granularcarbon cell, I may mention the condenser and the piezoelectric crystal.'Any such device may replace the granular carbon cell as shown hereinwithout departure from my invention.

Since in any case the mass and the stiffness of all the moving parts inthe system have very low effective values, the input impedance of thetranslating unit will be very low and in consequence in the case of aphonograph reproducer there will be very little destruction of the wallsof the record grooves. Consequently those forms of my inventionspecifically disclosed herein are particularly applicable forreproducing records engraved on wax wherein the stiffness of the recordwalls is very small. Furthermore, because of the high sensitivity of thegranular carbon cell as a translating medium, the sensitivity of thesetranslating units'has been found under equivalent conditions to be verymuch higher than a similar device using electro-magnetic translatingmedium and having approximately the same input impedance.

The value of the resistance R may vary considerably due to changes inviscosity of the fluid used and to expansion or contraction of themetallic parts of the translating unit. However, such variations willnot greatly affect the frequency characteristics of the device if thelimitations set forth herein are conservatively met. Such changes,however, will somewhat affect the sensitivity of the unit butsensitivity changes can be readily compensated and are therefore usuallyunimportant. If it is so desired, any of a number of variousarrangements may be employed for compensating for the change inviscosity or the change in dimensions of the parts. Such compensatingarrangements are disclosed in prior art relating to damping devices andare not therefore described herein.

Having thus described my invention, I claim:

1. A device for translating mechanical vibrations into correspondingelectrical current comprising a member for receiving mechanicalvibrations, translating means having a movable element, said meanshaving an output voltage proportional to the displacement of saidmovable element, and transmitting means between said member and saidmovable element for vibrating the latter with a sinusoidal displacementof constant amplitude over a range of frequencies when said memberreceives a sinusoidal vibration having constant maximum cyclic velocity.

2. In a device for translating mechanical vibratio-ns into correspondingelectrical currents, a vibration receiving member, and transmittingmeans actuatable by said member, which means is adapted to transmitsinusoidal force of constant amplitude over a range of audio frequencieswhen said member receives sinusoidal vibrations having constant maximumcyclic velocity.

3. In a translating device, vibration receiving means, translating meanscomprising a movable element and having an output voltage proportionalto the displacement of said element, and means for transmittingvibrations from said receiving means to said element, said transmittingmeans having a force reaction directly proportional to the velocity onlyof the vibrations impressed thereon.

r 4. An electrical phonographicrepro-ducer comprising a vibrationreceiving member, means cooperative with said member and consisting of asubstantially pure mechanical resistance for transmitting vibratoryforces, and translating means having a movable element to receive saidvibratory forces and having an impedance higher than that of saidtransmitting means over most of the range of frequencies to bereproduced.

5. An electrical phonographic reproducer comprising a stylus forengagement with a record groove, a member resiliently supporting saidstylus, translating means having a movable element, and transmittingmeans between said member and said element, said transmitting meansimpressing forces on said element proportional to the velocity of saidmember when the member, is driven at sound frequencies.

6. An electrical phonographic reproducer comprising a stylus forengagement with a record groove, a member resiliently supporting saidstylus, translating means comprising a movable element and having anoutput voltage proportional to the displacement of said movable element,and transmitting means between said member and said element, saidtransmitting means impressing forces on said element proportional to thevelocity of said member.

7. A translating unit comprising vibration receiving means including avibratile member, a translating medium having a movable element, andtransmitting means between said member and said element, saidtransmitting means impressing forces on said element proportional to thevelocity of said member when the member is driven at sound frequencies.

8. A translating unit comprising vibration receiving means, translatingmeans having a movable element and having an output voltage proportionalto the displacement of said movable element, and transmitting meansbetween said receiving means and said translating means, saidtransmitting means displacing said element in proportion to the velocityof said receiving means.

9. An audio frequency translating unit comprising resilient vibrationreceiving means, translating means having a movable element, andtransmitting means between said receiving means and said translatingmeans having a gap filled with viscous material, said gap being boundedon one side by a portion of said receiving means and on the other sideby a portion of said movable element, said portions being arranged tocoact with said viscous material to form a mechanical impedancecomprising chiefly resistance, said resistance having a smaller valuethan the impedance of said movable element over most of the range offrequencies to be transmitted.

10. A translating device comprising resilient vibration receiving means,a granular carbon cell having a movable electrode, and transmittingmeans between said receiving means and said cell, said transmittingmeans displacing said electrode in proportion to the velocity of saidvibration receiving means.

1l.'In a translating unit, resilient vibration receiving means, agranular carbon cell having a movable element comprising an electrode,and transmitting means between said receiving-means and said elementhaving a gap filled with viscous material, said gap being bounded on oneside by a portion of said receiving means and on the other side by aportion of said element, said portions being arranged to coact with saidviscous material to form a mechanical impedance comprising chieflyresistance.

12. In an electrical phonographic reproducer, a resilient member, astylus having connection with said member, a granular carbon cell havinga movable element, and transmitting means between said member and saidelement having a gap filled with viscous material, said gap beingbounded on one side by a portion of said diaphragm and on the other sideby a portion of said element, said portions being arranged to coact withsaid viscous material to form a mechanical impedance comprising chieflyresistance.

13. An electrical phonographic reproducer comprising a stylus, atranslating medium having a movable element, transmitting means having asmaller mechanical impedance than said element over most of the range offrequencies to be reproduced and comprising a pair of relatively movablespaced plates, the space between said plates being filled with viscousmaterial, said spaced plates being arranged to coact with said viscousmaterial to form a mechanical impedance due principally to the viscosityof said material, one of said spaced plates being connected to saidmovable element, and means to transmit vibrations from said stylus tothe other plate.

14. In a translating unit, vibration receiving means, a movable element,and a coupling means therebetween which when actuated by vibrationshaving a constant maximum cyclic velocity characteristic, producesvibrations in said element having a constant maximum cyclic amplitudecharacteristic.

15. A phonographic roproducer comprising a diaphragm, a stylus connectedwith said diaphragm, a granular carbon cell having a vibratablediaphragm, a light, stifi arm fastened to the latter diaphragm andhaving an end portion opposed to and spaced from said first nameddiaphragm, said arm rocking said carbon cell diaphragm about a diameterthereof when force is applied to said end portion, and viscous materialfilling the space between said end portion and the opposed diaphragm.

ORVILLE M. DUNNING.

